To date, the evaluation of the optical quality of the eye in clinical populations has been limited principally to measurements of visual performance (e.g., acuity, contrast sensitivity, and glare disability). While measures the visual performance, in particular contrast sensitivity, reflect important aspects of optical quality, they do not readily reflect changes in image quality as a function of pupil size nor give insight to the type of optical change that might have occurred in higher order aberrations of the eye. This is important, since pupil size (and therefore, the optical quality of the retinal image) varies considerably among individuals and within an individual as a function of ambient illumination. For example, while work has been done to specify changes in visual performance following radial keratotomy (RK) surgery, little or nothing is known about the changes in the eye's optical aberrations and the impact of these changes as a function of pupil size. The proposed research is designed to fill this information void and in the process test the general usefulness of aberration measurement in a clinical population by first, specifying the change in higher order monochromatic aberrations of the eye resulting from RK and, second, using the aberration measurements to predict visual performance as a function of pupil size. To accomplish this goal, measurements of higher order monochromatic aberrations of the eye will be made using the Howland crossed-cylinder aberroscope on 1) RK patients prior to, one week after, and at four month intervals for one year following surgery; and 2) age-matched normals following the same testing sequence. These data will be used: 1) To quantify the amount and degree of variation in higher order aberrations within and between normal and RK eye; 2) to predict optical performance as a function of pupil size; and 3) to compare predicted performance with actual visual performance as a function of pupil size.